You can follow the above instructions with only two primary partitions one boot partition

(required because of LVM), and one primary LVM partition. Within the LVM partition you can have
as many partitions as you need, but most importantly it should contain at least root, swap, and
home logical volume partitions. This has the added benefit of having only one keyfile for all
your partitions, and having the ability to hibernate your computer (suspend to disk) where the
swap partition is encrypted. If you decide to do so your hooks in /etc/mkinitcpio.conf
should look like
HOOKS=" ... usb usbinput (etwo or ssldec) encrypt(if using openssl) lvm2 resume ... "
and you should add "resume=/dev/mapper/<VolumeGroupName>-<LVNameOfSwap>" to your kernel parameters.

If you need to temporarily store the unecrypted keyfile somewhere, do not store them on an unencrypted disk. Even better make sure to store them to RAM such as /dev/shm.

If you want to use a GPG encrypted keyfile, you need to use a statically compiled GnuPG version 1.4 or you could edit the hooks and use this AUR package gnupg1

It is possible that an update to OpenSSL could break the custom ssldec mentioned in the second forum post.

Remote unlocking of the root (or other) partition

If you want to be able to reboot a fully LUKS-encrypted system remotely, or start it with a Wake-on-LAN service, you will need a way to enter a passphrase for the root partition/volume at startup. This can be achieved by running the net hook along with an SSH server in initrd. Install the dropbear_initrd_encryptAUR package from the AUR and follow the post-installation instructions. Replace the encrypt hook with dropbear encryptssh in /etc/mkinitcpio.conf. Put the net hook early in the HOOKS array if your DHCP server takes a long time to lease IP addresses.

If you would simply like a nice solution to mount other encrypted partitions (such as /home)remotely, you may want to look at this forum thread.

Modifying the encrypt hook for a non-root partition

Maybe you have a requirement for using the encrypt hook on a non-root partition. Arch does not support this out of the box, however, you can easily change the cryptdev and cryptname values in /lib/initcpio/hooks/encrypt (the first one to your /dev/sd* partition, the second to the name you want to attribute). That should be enough.

The big advantage is you can have everything automated, while setting up /etc/crypttab with an external key file (i.e. the keyfile is not on any internal hard drive partition) can be a pain - you need to make sure the USB/FireWire/... device gets mounted before the encrypted partition, which means you have to change the order of /etc/fstab (at least).

Of course, if the cryptsetup package gets upgraded, you will have to change this script again. Unlike /etc/crypttab, only one partition is supported, but with some further hacking one should be able to have multiple partitions unlocked.

If you want to do this on a software RAID partition, there is one more thing you need to do. Just setting the /dev/mdX device in /lib/initcpio/hooks/encrypt is not enough; the encrypt hook will fail to find the key for some reason, and not prompt for a passphrase either. It looks like the RAID devices are not brought up until after the encrypt hook is run. You can solve this by putting the RAID array in /boot/grub/menu.lst, like

kernel /boot/vmlinuz-linux md=1,/dev/hda5,/dev/hdb5

If you set up your root partition as a RAID, you will notice the similarities with that setup ;-). GRUB can handle multiple array definitions just fine:

Securing the unencrypted boot partition

Referring to an article from the ct-magazine (Issue 3/12, page 146, 01.16.2012 http://www.heise.de/ct/inhalt/2012/03/6/) the following script checks files under /boot for changes of SHA-1 hash, inode and occupied blocks on the hard drive. It also checks the MBR. The script cannot prevent certain type of attacks, but a lot are made harder. No configuration of the script itself is stored in unencrypted /boot. With a locked/powered-off crypted system this makes it infeasible for an attacker to recognize that an automatic checksum comparison of the partition is done upon boot.

There is a small caveat for systemd: At the time of writing the original chkboot.sh script provided contains an empty space at the beginning of #!/bin/bash which has to be removed for the service to start successfully.

As /usr/local/bin/chkboot_user.sh need to be excuted after login, add it to the autostart (e.g. under KDE -> System Settings -> Startup and Shutdown -> Autostart; Gnome3: gnome-session-properties).

With Arch Linux changes to /boot are pretty frequent, for example by new kernels rolling-in. Therefore it may be helpful to use the scripts with every full system update. One way to do so:

Alternatively to above scripts, a hash check can be set up with AIDE which can be customized via a very flexible configuration file.

While one of these methods should serve the purpose for most users, they do not address all security problems associated with the unencrypted /boot. One approach which endeavours to provide a fully authenticated boot chain was published with POTTS as an academic thesis to implement the STARK authentication framework.

The POTTS proof-of-concept uses Arch Linux as a base distribution and implements a system boot chain with

POTTS - a bootmenu for a one-time authentication message prompt

TrustedGrub - a grub-legacy implementation which authenticates the kernel and initramfs against TPM chip registers

TRESOR - a kernel patch which implements AES but keeps the master-key not in RAM but in CPU registers during runtime.

As part of the thesis installation instructions based on Arch Linux (iso 2013-01) have been published. If you want to try it, be aware these tools are not in standard repositories and the solution will be time consuming to maintain.